Following lesions of the rat nucleus basalis of Meynert, there was an acute (1 week) increase in the number of M2 muscarinic binding sites which returned to normal after 3 months. On the other hand, M1 muscarinic receptors were normal at 1 week but decreased at 3 months. These changes were bilateral despite the lesion being unilateral. These results suggest that there are complex changes in cortical cholinergic receptors following degeneration of cortical cholinergic input. Nerve growth factor (NGF) receptors were identified in the human cerebral cortex and had a dissociation constant (Kd) very similar to the cholinergic-specific NGF receptors recently described in the rat brain. Autoradiographic methods were established to identify receptor binding sites in large sections of the human brain. Procedures were established to obtain rapid autopsies on inpatients and outpatients who die, and for preparing brain tissue for diagnosis and chemical and neurochemical analysis.